JP6315600B2 - Semiconductor optical device - Google Patents

Description

  The present invention relates to a semiconductor optical device applicable to a semiconductor laser, a semiconductor optical amplifier, or the like used for a light source for an optical transmitter.

  Due to the explosive increase in the amount of network traffic accompanying the spread of the Internet, optical fiber transmission continues to increase in speed and capacity. Among these, the semiconductor laser has been continuously developed as a light source device that supports optical fiber communication. In particular, the realization of a single-mode light source using a distributed-feedback (DFB) laser has greatly contributed to speeding up and increasing the capacity of optical fiber communication by time division multiplexing and wavelength division multiplexing.

  However, the increase in capacity by the conventional multiplexing technique is approaching the limit, and in recent years, multi-level modulation schemes excellent in frequency use efficiency and dispersion tolerance have been studied. Currently, research and development of multi-level phase modulation such as QPSK (quadrature phase-shift keying) and digital coherent system for receiving phase-modulated signals has progressed, and multi-level phase modulation system is used. 40G and 100G systems are in practical use. At the research level, in addition to the phase modulation method, the progress of the amplitude phase modulation method is remarkable.

  One of the key devices for receiving these multilevel modulations is a semiconductor laser used as a transmitter and local light on the receiving side. In particular, since interference is used to receive a phase modulation signal by the digital coherent method, the phase noise of the light source, that is, the line width characteristic of the light source greatly affects the reception characteristic. Therefore, it is desirable that the line width of the light source is as narrow as possible. The current 100G system is required to have a frequency of 1 MHz or less, and in the future, a line width of 100 kHz or less is expected.

  Up to now, various studies have been made for suppressing the line width of a semiconductor laser. The line width Δν of the semiconductor laser is expressed as follows based on the extended Showlow Towns relational expression by Henry.

In the equation (1), h is Planck's constant, [nu oscillation frequency, P0 is the laser output, v _g is the group velocity, alpha _m resonator loss, alpha ₀ is guided Michison, F is the output coefficient, K is Petermann's factor, L _a is the active layer length, L _p is the cavity length, n _sp is the luminescence recombination constant, and α is the line width enhancement factor.

For example, since it is possible to readily linewidth suppressed to reduce the ratio of the active layer L _a to the total cavity length L _p, narrow linewidth laser using an external resonator One powerful technique It is. So far, a waveguide resonator structure (see Non-Patent Document 1) or a spatial resonator structure (see Non-Patent Document 2) has been reported, and a laser with a line width of 100 kHz or less has been realized.

However, a laser using an external resonator has problems in making a single mode and stabilizing the oscillation wavelength. In addition, since the element size is increased, there are significant problems for future large-scale integration. For this reason, a narrow linewidth laser capable of semiconductor monolithic integration is desired. As a main approach, a technique for suppressing the resonator loss α _m is employed.

  Suppressing the resonator loss can be restated as reducing the mode threshold gain coefficient and increasing the photon lifetime in the resonator. That is, it is only necessary that light can be confined in the resonator for a long time. For this reason, approaches have been taken to increase the resonator length and lower the threshold gain coefficient. To suppress the resonator loss in the λ / 4 shift type DFB laser, there are two approaches: a method of increasing the coupling coefficient κ of the DFB diffraction grating and a method of increasing the active layer length L.

  However, if κL is increased, the effect of spatial hole burning increases, and the carrier distribution in the resonator becomes non-uniform. As a result, the effective refractive index distribution becomes large and single mode oscillation cannot be obtained. Therefore, generally, the value of κL is limited to about 1.5, and the active layer length L is increased to lower the threshold gain coefficient. So far, a line width of 160 kHz has been realized in a λ / 4 shift DFB laser with an element length of 1500 μm (see Non-Patent Document 3).

  However, if the cavity loss of the semiconductor laser is suppressed, the light stays in the cavity for a long time, making it more susceptible to waveguide loss, making it difficult to extract the light and obtaining a sufficient light output. There was no problem. Therefore, reducing the loss of the optical waveguide is a major issue for narrowing the linewidth of the semiconductor laser.

  A conventional semiconductor laser has a structure in which a cladding layer doped with impurities is formed above and below an active layer, and current is injected in a vertical direction (a direction perpendicular to the substrate surface). In particular, a buried structure for efficiently injecting current into the active layer is a typical structure. This semiconductor laser will be described with reference to FIG. FIG. 21 is a cross-sectional view showing a configuration of a conventional pn buried type semiconductor laser. In this semiconductor laser, a clad layer 602 made of n-type InP is laminated on a substrate 601 made of n-type InP, and an active layer 603 is formed thereon.

Both sides of the cladding layer 602 and the active layer 603 are buried with a buried layer 604 made of p-InP. A current blocking layer 605 made of an n-InP layer is formed on the buried layer 604. Over the active layer 603 and the current blocking layer 605, an over clad layer 606 made of p-InP and a contact layer 607 made of p-InGaAs are formed. The clad layer 602, the active layer 603, and the over clad layer 606 constitute an optical waveguide. An insulating layer 608 made of SiO ₂ is formed on the contact layer 607 in the upper region of the current blocking layer 605. A p-electrode 611 that is in ohmic contact with the contact layer 607 is formed between the insulating layers 608, and an n-electrode 612 is in ohmic contact with the back surface of the substrate 601.

K. Nemoto et al., "Narrow-Spectral-Linewidth Wavelength-Tunable Laser Diode with Si Wire Waveguide Ring Resonators", Applied Physics Express, vol.5, 082701, 2012. N. Wang et al., "Narrow-Linewidth Tunable Lasers With Retro-Reflective External Cavity", IEEE PHOTONICS TECHNOLOGY LETTERS, vol.24, no.18, pp.1591-1593, 2012. H. Ishii et al., "Narrow spectral linewidth operation (<160 kHz) in widely tunable distributed feedback laser array", ELECTRONICS LETTERS, vol.40, no.10, 2010. S. R. Jain et al., "Integrated Hybrid Silicon Transmitters", JOURNAL OF LIGHTWAVE TECHNOLOGY, vol.30, no.5, pp.671-678, 2012.

  However, the above-described embedded laser has a problem that the waveguide loss is large. In the pn buried structure, both sides and the upper part of the active layer 603 are composed of a p-type semiconductor having a high hole absorption amount. Therefore, as shown in a region 613 in FIG. This is a major cause of propagation loss. FIG. 23 shows the calculation result of the optical confinement coefficient of the active layer and the p-type semiconductor region in the pn buried waveguide structure in which the active layer has a six-layer quantum well structure. In FIG. 23, (a) shows the calculation result of the optical confinement coefficient of the quantum well layer of the active layer, and (b) shows the calculation result of the optical confinement coefficient of the p-type semiconductor region. The active layer width is changed from 0.5 μm to 1.6 μm.

The optical confinement in the p semiconductor region is over 35% for all waveguide widths. The absorption coefficient of p-type InP is about 20 cm ⁻¹ per doping concentration of 1 × 10 ¹⁸ cm ^-3 . Therefore, for example, when the doping concentration of the p-type semiconductor is 1 × 10 ¹⁸ cm ⁻³ , the loss in the p-type semiconductor alone reaches 7 to 10 cm ⁻¹ . Therefore, reduction of propagation loss in the p-type semiconductor region around the active layer is an important issue.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to reduce waveguide loss in a semiconductor optical device having a buried waveguide structure.

A semiconductor optical device according to the present invention includes an optical waveguide formed of a core formed on a substrate, an active layer disposed in a state capable of being optically coupled to the core by extending a predetermined distance in the waveguide direction of the optical waveguide. A p-type semiconductor layer and an n-type semiconductor layer formed in contact with the active layer, a semiconductor layer formed in contact with at least one of the lower surface and the upper surface of the active layer, an n-type electrode connected to the n-type semiconductor layer, A p-type electrode connected to the p-type semiconductor layer, and the p-type semiconductor layer and the n-type semiconductor layer are formed with the active layer sandwiched in a direction parallel to the plane of the substrate. current is injected in a direction parallel to the core, that is formed apart from the p-type semiconductor layer.

In the semiconductor optical device, the core is disposed between the substrate and the active layer. The semiconductor layer formed in contact with the upper surface of the active layer has a side surface in contact with the p-type semiconductor layer and the n-type semiconductor layer and is p-type.

  In the semiconductor optical device, the core is disposed on the active layer as viewed from the substrate side.

In the semiconductor optical device, the side surface of the semiconductor layer formed in contact with the lower surface of the active layer is in contact with the p-type semiconductor layer and the n-type semiconductor layer and is p-type .

In the semiconductor optical device, p-type semiconductor layer contact and the n-type semiconductor layer may be on so that is formed from InP.

  As described above, according to the present invention, it is possible to obtain an excellent effect that waveguide loss in a semiconductor optical device having a buried waveguide structure can be reduced.

FIG. 1A is a cross-sectional view showing a semiconductor optical device according to Embodiment 1 of the present invention. FIG. 1B is a perspective view showing the semiconductor optical device in the first embodiment of the present invention. FIG. 2A is an explanatory diagram for explaining the electric field distribution of the semiconductor optical device according to the first embodiment of the present invention. FIG. 2B is a distribution diagram showing a calculation result of the electric field distribution of the semiconductor optical device in the first embodiment of the present invention. FIG. 3A is a characteristic diagram showing the active layer width dependence of optical confinement in the p-type semiconductor layer 106. FIG. 3B is a characteristic diagram showing the active layer width dependency of light confinement in the active layer 103. FIG. 4 is a characteristic diagram showing a calculation result of the light output dependency of the laser line width in the conventional structure (a) and the semiconductor optical device (b) in the first embodiment. FIG. 5 is a sectional view showing a semiconductor optical device according to the second embodiment of the present invention. FIG. 6 is a sectional view showing a semiconductor optical device according to the third embodiment of the present invention. FIG. 7 is a sectional view showing a semiconductor optical device according to the fourth embodiment of the present invention. FIG. 8A is a sectional view showing a semiconductor optical device according to the fifth embodiment of the present invention. FIG. 8B is a perspective view showing a semiconductor optical device in the fifth embodiment of the present invention. FIG. 9A is an explanatory diagram for explaining the electric field distribution of the semiconductor optical device in the fifth embodiment of the present invention. FIG. 9B is a distribution diagram showing the calculation result of the electric field distribution of the semiconductor optical device in the fifth embodiment of the present invention. FIG. 10A is a characteristic diagram showing the active layer width dependence of optical confinement in the p-type semiconductor layer 206. FIG. 10B is a characteristic diagram showing the active layer width dependency of light confinement in the active layer 203. FIG. 11 is a sectional view showing a semiconductor optical device according to the sixth embodiment of the present invention. FIG. 12 is a sectional view showing a semiconductor optical device according to the seventh embodiment of the present invention. FIG. 13 is a sectional view showing a semiconductor optical device according to the eighth embodiment of the present invention. FIG. 14A is a characteristic diagram showing the active layer width dependence of optical confinement in the p-type semiconductor layer 306. FIG. 14B is a characteristic diagram showing the dependency of light confinement in the active layer 303 on the active layer width. FIG. 15 is a sectional view showing a semiconductor optical device according to the ninth embodiment of the present invention. FIG. 16 is a sectional view showing a semiconductor optical device according to the tenth embodiment of the present invention. FIG. 17 is a sectional view showing a semiconductor optical device according to the eleventh embodiment of the present invention. FIG. 18 is a sectional view showing a semiconductor optical device according to the twelfth embodiment of the present invention. FIG. 19 is a sectional view showing a semiconductor optical device according to the thirteenth embodiment of the present invention. FIG. 20 is a sectional view showing a semiconductor optical device according to the fourteenth embodiment of the present invention. FIG. 21 is a cross-sectional view showing a configuration of a conventional pn buried type semiconductor laser. FIG. 22 is an explanatory diagram for explaining the electric field distribution of a conventional pn buried type semiconductor laser. FIG. 23 is a characteristic diagram showing the calculation result of the optical confinement coefficient between the active layer and the p-type semiconductor region in the pn buried waveguide structure in which the active layer has a six-layer quantum well structure in a conventional pn buried type semiconductor laser. It is.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIGS. 1A and 1B. FIG. 1A is a cross-sectional view showing a semiconductor optical device according to Embodiment 1 of the present invention. FIG. 1B is a perspective view showing the semiconductor optical device according to Embodiment 1 of the present invention.

  The semiconductor optical device includes an optical waveguide 121 including a clad layer 101 and a core 102 formed on a substrate 100. The core 102 is embedded in the cladding layer 101. In addition, the active layer 103 includes a active layer 103 that extends in a waveguide direction of the optical waveguide 121 and is optically coupled to the core 102, and a semiconductor layer 104 that is formed on the active layer 103. In addition, an n-type semiconductor layer 105 and a p-type semiconductor layer 106 are provided which are in contact with the active layer 103 and the semiconductor layer 104 and sandwich the active layer 103 and the semiconductor layer 104 therebetween. In the first embodiment, the core 102 is disposed between the substrate 100 and the active layer 103. In the first embodiment, current is injected into the active layer 103 in a direction parallel to the plane of the substrate 100.

  In the first embodiment, the active layer 103 described above is disposed on the optical waveguide 121 when viewed from the substrate 100.

  Further, an n-type electrode 109 connected to the n-type semiconductor layer 105 through the contact layer 107 and a p-type electrode 110 connected to the p-type semiconductor layer 106 through the contact layer 108 are provided. The p-type semiconductor layer 106 and the n-type semiconductor layer 105 are formed with the active layer 103 sandwiched in a direction parallel to the plane of the substrate 100.

  In the first embodiment, the diffraction grating pattern 132 is formed on the upper surface of the semiconductor layer 104 in the resonator region 131 having a predetermined length in the extending direction of the optical waveguide 121, and the distributed Bragg reflection structure has a wavelength of 1.55 μm. Is configured. Although not shown in FIG. 1B, the upper surfaces of the semiconductor layer 104, the n-type semiconductor layer 105, and the p-type semiconductor layer 106 between the contact layer 107 and the contact layer 108 are protected by a protective film 111. In the semiconductor optical device according to the first embodiment, a non-reflective film (not shown) is formed at both ends of the resonator region 131 to constitute a distributed feedback laser.

  The substrate 100 and the clad layer 101 are made of, for example, InP made semi-insulating by doping iron, and the core 102 is made of InGaAsP. The active layer 103 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked. The emission wavelength of the active layer 103 is 1.55 μm.

Further, for example, the semiconductor layer 104 is made of undoped InP (i-InP), and the n-type semiconductor layer 105 is an n-type InP (n-InP) doped with Si of about 1 × 10 ¹⁸ cm ^−3. The p-type semiconductor layer 106 is made of p-type InP (p-InP) doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 107 is made of n-type InGaAs (n-InGaAs) doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 108 is doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. InGaAs (p-InGaAs). Further, the protective film 111 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 105 and the p-type semiconductor layer 106 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 103 and the semiconductor layer 104 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  Next, characteristics of the semiconductor optical device in the first embodiment will be described. First, the electric field distribution will be described. In the semiconductor optical device according to the first embodiment, as shown in FIG. 2A (elliptical region) and FIG. 2B (calculation result of electric field distribution), the electric field is distributed around the core 102. Thus, most of the electric field strength exists in the region of the core 102 below the active layer with low propagation loss, and the overlap between the electric field and the p-type semiconductor layer 106 is very small.

  Next, the dependence of light confinement around the active layer 103 on the active layer width will be described with reference to FIGS. 3A and 3B. FIG. 3A shows the active layer width dependency of light confinement in the p-type semiconductor layer 106, and FIG. 3B shows the active layer width dependency of light confinement in the active layer 103. The band gap wavelength of the core 102 was 1.3 μm or 1.4 μm, and the thickness of the core 102 was 300 nm. The distance between the active layer 103 and the core 102 was 100 nm, and the thickness of the semiconductor layer 104 disposed on the active layer 103 was 200 nm.

  In any configuration, the optical confinement in the p-type semiconductor layer 106 is 2.5% or less, and is reduced to 1/10 or less as compared with the pn buried structure. The optical confinement of the active layer 103 is 2.5 to 5%, which is comparable to the pn buried structure, and sufficient optical confinement for laser oscillation can be obtained. In addition, although the optical confinement of the active layer 103 increases and the loss in the p-type semiconductor layer 106 also decreases as the active layer width increases, the width of the active layer 103 is considered in consideration of the uniformity of lateral carrier injection. Is desirably 1 μm or less.

Next, the light output dependency of the laser line width will be described with reference to FIG. FIG. 4 is a calculation result of the light output dependence of the laser line width in the conventional structure (a) and the semiconductor optical device (b) in the first embodiment. Formula (1) was used for the calculation. In the first embodiment, the active layer width is 1 μm, and the band gap wavelength of the core 102 is 1.3 μm. The laser resonator had a κL of 1.5 and a resonator length of 1500 μm. The linewidth enhancement factor alpha 5, the group refractive index v _g 4.2, Petermann's factor K is 2, the output factor F 0.5, the spontaneous emission factor n _sp is 1.

In the conventional structure, the loss of the p-type semiconductor region is 10 cm ⁻¹ and the other loss is 5 cm ⁻¹ . On the other hand, in Embodiment 1, since the optical confinement of the p-type semiconductor layer 106 is 1% from FIG. 3A, the loss in this region is 0.2 cm ⁻¹ . Therefore, the loss of the p-type semiconductor region in the first embodiment is almost negligible as compared with the other loss of 5 cm ⁻¹ . The light output efficiency is increased by reducing the light loss, and the line width is greatly reduced when compared with the same light output. A line width of 100 kHz or less was obtained even at an output of 20 mW or less. Thus, according to the first embodiment, an active layer waveguide with low propagation loss is realized. By applying this active layer waveguide to a semiconductor laser, a narrow linewidth laser can be realized.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 5 is a sectional view showing a semiconductor optical device according to the second embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 121 including a clad layer 101 and a core 102 formed on a substrate 100. The core 102 is embedded in the cladding layer 101. In addition, the active layer 103 is provided with a predetermined distance extending in the waveguide direction of the optical waveguide 121 and arranged to be optically coupled to the core 102, and a semiconductor layer 154 formed on the active layer 103. The n-type semiconductor layer 105 and the p-type semiconductor layer 106 are provided in contact with the active layer 103 and the semiconductor layer 154 so as to sandwich the active layer 103 and the semiconductor layer 154. In the second embodiment, the core 102 is disposed between the substrate 100 and the active layer 103. Also in the second embodiment, current is injected into the active layer 103 in a direction parallel to the plane of the substrate 100.

  In the second embodiment, the above-described active layer 103 is disposed on the optical waveguide 121 when viewed from the substrate 100.

  Further, an n-type electrode 109 connected to the n-type semiconductor layer 105 through the contact layer 107 and a p-type electrode 110 connected to the p-type semiconductor layer 106 through the contact layer 108 are provided. The p-type semiconductor layer 106 and the n-type semiconductor layer 105 are formed with the active layer 103 sandwiched in a direction parallel to the plane of the substrate 100.

  Also in the second embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the semiconductor layer 154 in the resonator region having a predetermined length in the extending direction of the optical waveguide 121, and has a wavelength distribution of 1.55 μm. A Bragg reflection structure is configured. In addition, the upper surfaces of the semiconductor layer 154, the n-type semiconductor layer 105, and the p-type semiconductor layer 106 between the contact layer 107 and the contact layer 108 are protected by a protective film 111. The semiconductor optical device according to the second embodiment also forms a distributed feedback laser by forming a non-reflective film (not shown) at both ends of the resonator region.

  The substrate 100 and the cladding layer 101 are made of, for example, semi-insulating InP, and the core 102 is made of InGaAsP. The active layer 103 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked. The emission wavelength of the active layer 103 is 1.55 μm.

Also in the second embodiment, for example, the n-type semiconductor layer 105 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and the p-type semiconductor layer 106 is made of 1 × 10 ¹⁸ Zn. It is composed of p-InP doped with about cm ⁻³ . Here, in the second embodiment, the semiconductor layer 154 is made of, for example, p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 107 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 108 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. Further, the protective film 111 is made of, for example, SiO ₂ .

  The above structure is the same as that of the first embodiment except for the semiconductor layer 154. In the second embodiment, a p-type semiconductor layer 154 is disposed on the active layer 103. In the configuration of the first and second embodiments, the lateral injection structure is formed by the n-type semiconductor layer 105 and the p-type semiconductor layer 106 sandwiching the active layer 103 in the substrate plane direction. In this lateral injection structure, there is a problem that hole injection becomes non-uniform. To solve this problem, the second embodiment uses the p-type semiconductor layer 154, so that uniform current injection can be performed in the lateral direction even when the waveguide width is wide. Since the electric field is mostly present in the waveguide region, there is little overlap between the p-type semiconductor layer 154 and the electric field, and the current injection efficiency can be increased without worrying about an increase in the waveguide loss.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 6 is a sectional view showing a semiconductor optical device according to the third embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 121 including a clad layer 101 and a core 152 formed on a substrate 100. In the third embodiment, the core 152 has a layered structure and has a slab waveguide structure. In addition, the active layer 103 includes a semiconductor layer 104 formed on the active layer 103, and an active layer 103 that extends in a waveguide direction of the optical waveguide 121 and is disposed so as to be optically coupled to the core 152. In addition, an n-type semiconductor layer 105 and a p-type semiconductor layer 106 are provided which are in contact with the active layer 103 and the semiconductor layer 104 and sandwich the active layer 103 and the semiconductor layer 104 therebetween. In the third embodiment, the core 152 is disposed between the substrate 100 and the active layer 103. Also in the third embodiment, current is injected into the active layer 103 in a direction parallel to the plane of the substrate 100.

  In the third embodiment, the above-described active layer 103 is disposed on the optical waveguide 121 when viewed from the substrate 100.

  Further, an n-type electrode 109 connected to the n-type semiconductor layer 105 through the contact layer 107 and a p-type electrode 110 connected to the p-type semiconductor layer 106 through the contact layer 108 are provided. The p-type semiconductor layer 106 and the n-type semiconductor layer 105 are formed with the active layer 103 sandwiched in a direction parallel to the plane of the substrate 100.

  Also in the third embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the semiconductor layer 104 in the resonator region having a predetermined length in the extending direction of the optical waveguide 121, and has a wavelength distribution of 1.55 μm. A Bragg reflection structure is configured. The upper surfaces of the semiconductor layer 104, the n-type semiconductor layer 105, and the p-type semiconductor layer 106 between the contact layer 107 and the contact layer 108 are protected by a protective film 111. The semiconductor optical device in the third embodiment also forms a distributed feedback laser by forming a non-reflective film (not shown) at both ends of the resonator region.

  The substrate 100 and the clad layer 101 are made of, for example, semi-insulating InP, and the core 152 is made of InGaAsP. The active layer 103 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked. The emission wavelength of the active layer 103 is 1.55 μm.

In the third embodiment, for example, the semiconductor layer 104 is made of i-InP, the n-type semiconductor layer 105 is made of n-InP doped with Si of about 1 × 10 ¹⁸ cm ⁻³ , and p The type semiconductor layer 106 is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 107 is made of n-type n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 108 is p− doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. It is composed of InGaAs. Further, the protective film 111 is made of, for example, SiO ₂ .

  The above configuration is the same as that of the first embodiment except for the core 152. According to the third embodiment, since the core 152 does not have an embedded structure, an embedding process is unnecessary, and device fabrication is facilitated.

[Embodiment 4]
Next, Embodiment 4 of the present invention will be described with reference to FIG. FIG. 7 is a sectional view showing a semiconductor optical device according to the fourth embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 121 including a clad layer 101 a, a clad layer 112, and a core 102 formed on a substrate 100. In the fourth embodiment, the clad layer 101a is a lower clad and the clad layer 112 is an upper clad. In addition, the active layer 103 includes a active layer 103 that extends in a waveguide direction of the optical waveguide 121 and is optically coupled to the core 102, and a semiconductor layer 104 that is formed on the active layer 103.

  In addition, an n-type semiconductor layer 105 and a p-type semiconductor layer 106 are provided which are in contact with the active layer 103 and the semiconductor layer 104 and sandwich the active layer 103 and the semiconductor layer 104 therebetween. Also in the fourth embodiment, the core 102 is disposed between the substrate 100 and the active layer 103. In the fourth embodiment, current is injected into the active layer 103 in a direction parallel to the plane of the substrate 100.

  In the fourth embodiment, the above-described active layer 103 is disposed on the optical waveguide 121 when viewed from the substrate 100.

  Further, an n-type electrode 109 connected to the n-type semiconductor layer 105 through the contact layer 107 and a p-type electrode 110 connected to the p-type semiconductor layer 106 through the contact layer 108 are provided. The p-type semiconductor layer 106 and the n-type semiconductor layer 105 are formed with the active layer 103 sandwiched in a direction parallel to the plane of the substrate 100. For convenience of explanation, the substrate 100 and the clad layer 101a will be described separately, but these are integrally formed.

  In the fourth embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the semiconductor layer 104 in the resonator region having a predetermined length in the extending direction of the optical waveguide 121, and a distributed Bragg having a wavelength of 1.55 μm. A reflective structure is constructed. The upper surfaces of the semiconductor layer 104, the n-type semiconductor layer 105, and the p-type semiconductor layer 106 between the contact layer 107 and the contact layer 108 are protected by a protective film 111. The semiconductor optical device according to the fourth embodiment also forms a distributed feedback laser by forming a non-reflective film (not shown) at both ends of the resonator region.

  The substrate 100 and the clad layer 101a are made of, for example, semi-insulating InP, and the core 102 is made of InGaAsP. The cladding layer 112 is made of undoped InP. The active layer 103 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked. The emission wavelength of the active layer 103 is 1.55 μm.

Further, for example, the semiconductor layer 104 is made of i-InP, the n-type semiconductor layer 105 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and the p-type semiconductor layer 106 is It is composed of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 107 is made of n-type n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 108 is p− doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. It is composed of InGaAs. Further, the protective film 111 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 105 and the p-type semiconductor layer 106 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 103 and the semiconductor layer 104 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  In the fourth embodiment, since the core 102 is embedded with the cladding layer 112 made of undoped InP, the current insulation is lower than that of the semi-insulating InP, but the core 102 is made of the semi-insulating layer InP. Since an embedding process is unnecessary, device fabrication is facilitated. In particular, after forming the core 102 and the active layer 103, the active layer shape is formed in a lump, and then embedded with undoped InP, and Si is implanted into undoped InP to form the n-type semiconductor layer 105, and Zn diffusion implantation is performed. Then, if the p-type semiconductor layer 106 is formed, it can be formed by a single buried growth.

[Embodiment 5]
Next, Embodiment 5 of the present invention will be described with reference to FIGS. 8A and 8B. FIG. 8A is a sectional view showing a semiconductor optical device according to the fifth embodiment of the present invention. FIG. 8B is a perspective view showing the semiconductor optical device in the fifth embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 221 including a clad layer 204 and a core 202 formed on a substrate 201. The core 202 is embedded in the cladding layer 204. In addition, the active layer 203 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 221 and to be optically coupled to the core 202. Further, an n-type semiconductor layer 205 and a p-type semiconductor layer 206 are provided in contact with the active layer 203 and the clad layer 204 so as to sandwich the active layer 203 and the clad layer 204. In the fifth embodiment, the core 202 is disposed on the active layer 203 when viewed from the substrate 201 side. In the fifth embodiment, current is injected into the active layer 303 in a direction parallel to the plane of the substrate 201.

  In the fifth embodiment, the active layer 203 described above is disposed between the substrate 201 and the optical waveguide 221.

  Further, an n-type electrode 209 connected to the n-type semiconductor layer 205 through the contact layer 207 and a p-type electrode 210 connected to the p-type semiconductor layer 206 through the contact layer 208 are provided. The p-type semiconductor layer 206 and the n-type semiconductor layer 205 are formed with the active layer 203 sandwiched in a direction parallel to the plane of the substrate 201.

  In the fifth embodiment, the diffraction grating pattern 232 is formed on the upper surface of the cladding layer 204 in the resonator region 231 having a predetermined length in the extending direction of the optical waveguide 221, and the distributed Bragg reflection structure having a wavelength of 1.55 μm. Is configured. Although omitted in FIG. 8B, the upper surfaces of the cladding layer 204, the n-type semiconductor layer 205, and the p-type semiconductor layer 206 between the contact layer 207 and the contact layer 208 are protected by a protective film 211. In the semiconductor optical device according to the fifth embodiment, a non-reflective film (not shown) is formed at both ends of the resonator region 231 to constitute a distributed feedback laser.

  The substrate 201 is made of, for example, semi-insulating InP, and the core 202 is made of InGaAsP. The active layer 203 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier layer with a thickness of 9 nm are stacked. The emission wavelength of the active layer 203 is 1.55 μm.

Further, for example, the cladding layer 204 is made of semi-insulating InP, the n-type semiconductor layer 205 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and the p-type semiconductor layer 206. Is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 207 is made of n-type n-InGaAs doped with Si by about 1 × 10 ¹⁹ cm ⁻³ , and the contact layer 208 is p− doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. It is composed of InGaAs. The protective film 211 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 205 and the p-type semiconductor layer 206 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 203 and the cladding layer 204 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  Next, the characteristics of the semiconductor optical device in the fifth embodiment will be described. First, the electric field distribution will be described. In the semiconductor optical device in the fifth embodiment, an electric field is distributed around the core 202 as shown in FIGS. 9A (elliptical region) and 9B (calculation result of electric field distribution). Thus, most of the electric field strength exists in the region of the core 202 above the active layer with low propagation loss, and the overlap between the electric field and the p-type semiconductor layer 206 is very small.

  Next, the dependence of light confinement around the active layer 203 on the active layer width will be described with reference to FIGS. 10A and 10B. FIG. 10A shows the active layer width dependency of light confinement in the p-type semiconductor layer 206, and FIG. 10B shows the active layer width dependency of light confinement in the active layer 203. The band gap wavelength of the core 202 was 1.3 μm or 1.4 μm, and the thickness of the core 202 was 350 nm. The distance between the active layer 203 and the core 202 was 100 nm, and the thickness of the clad layer 204 disposed on the active layer 203 was 100 nm. The interval between the core 202 and the p-type semiconductor layer 206 was 500 nm.

  In any configuration, the optical confinement in the p-type semiconductor layer 206 is 1.5% or less, which is reduced to 1/10 or less as compared with the pn buried structure. The optical confinement of the active layer 203 is 7% or more, which is a significant improvement over the first embodiment. As described above, also in the fifth embodiment, by reducing the loss in the p-type semiconductor layer 206, a laser with high output, high efficiency, and narrow line width can be realized.

[Embodiment 6]
Next, Embodiment 6 of the present invention will be described with reference to FIG. FIG. 11 is a sectional view showing a semiconductor optical device according to the sixth embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 221 including a clad layer 254 and a core 202 formed on a substrate 201. The core 202 is embedded in the cladding layer 254. In addition, the active layer 203 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 221 and to be optically coupled to the core 202. In addition, an n-type semiconductor layer 205 and a p-type semiconductor layer 206 are provided in contact with the active layer 203 and the cladding layer 254 so as to sandwich the active layer 203 and the cladding layer 254. Also in the sixth embodiment, the core 202 is disposed on the active layer 203 when viewed from the substrate 201 side. Also in the sixth embodiment, current is injected into the active layer 303 in a direction parallel to the plane of the substrate 201.

  Here, the active layer 203, the n-type semiconductor layer 205, and the p-type semiconductor layer 206 also constitute an optical waveguide. In this optical waveguide according to the sixth embodiment, the active layer 203 is a core, and the substrate 201, the cladding layer 254, the n-type semiconductor layer 205, and the p-type semiconductor layer 206 are cladding. In the sixth embodiment, the above-described optical waveguide is disposed between the substrate 201 and the optical waveguide 221.

  Further, an n-type electrode 209 connected to the n-type semiconductor layer 205 through the contact layer 207 and a p-type electrode 210 connected to the p-type semiconductor layer 206 through the contact layer 208 are provided. The p-type semiconductor layer 206 and the n-type semiconductor layer 205 are formed with the active layer 203 sandwiched in a direction parallel to the plane of the substrate 201.

  Also in the sixth embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the cladding layer 254 in the resonator region having a predetermined length in the extending direction of the optical waveguide 221, and a distributed Bragg having a wavelength of 1.55 μm. A reflective structure is constructed. Note that the upper surfaces of the cladding layer 254, the n-type semiconductor layer 205, and the p-type semiconductor layer 206 between the contact layer 207 and the contact layer 208 are protected by a protective film 211. The semiconductor optical device according to the sixth embodiment also forms a distributed feedback laser by forming non-reflective films (not shown) at both ends of the resonator region.

  The substrate 201 is made of, for example, semi-insulating InP, and the core 202 is made of InGaAsP. The active layer 203 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier layer with a thickness of 9 nm are stacked. The emission wavelength of the active layer 203 is 1.55 μm.

For example, the n-type semiconductor layer 205 is made of n-InP doped with Si by about 1 × 10 ¹⁸ cm ⁻³ , and the p-type semiconductor layer 206 is doped with Zn by about 1 × 10 ¹⁸ cm ^−3. P-InP. Here, in the sixth embodiment, unlike the above-described fifth embodiment, the cladding layer 254 is made of undoped InP.

The contact layer 207 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 208 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. The protective film 211 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 205 and the p-type semiconductor layer 206 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 203 and the cladding layer 254 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  The above configuration is the same as that of the fifth embodiment described above except for the cladding layer 254. In the sixth embodiment, the clad layer 254 is made of undoped InP, and the current insulation is lower than that of the semi-insulating InP, but the fabrication becomes easy.

[Embodiment 7]
Next, Embodiment 7 of the present invention will be described with reference to FIG. FIG. 12 is a sectional view showing a semiconductor optical device according to the sixth embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 221 including a clad layer 204 and a core 202 formed on a substrate 201. The core 202 is embedded in the cladding layer 204. In addition, the active layer 203 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 221 and to be optically coupled to the core 202. Further, an n-type semiconductor layer 205 and a p-type semiconductor layer 206 are provided in contact with the active layer 203 and the clad layer 204 so as to sandwich the active layer 203 and the clad layer 204. Also in the seventh embodiment, the core 202 is disposed on the active layer 203 when viewed from the substrate 201 side. In Embodiment 7, a p-type semiconductor layer 212 is provided between the core 202 and the substrate 201. Also in the seventh embodiment, current is injected into the active layer 303 in a direction parallel to the plane of the substrate 201.

  In the seventh embodiment, the active layer 203 described above is disposed between the substrate 201 and the optical waveguide 221.

  Further, an n-type electrode 209 connected to the n-type semiconductor layer 205 through the contact layer 207 and a p-type electrode 210 connected to the p-type semiconductor layer 206 through the contact layer 208 are provided. The p-type semiconductor layer 206 and the n-type semiconductor layer 205 are formed with the active layer 203 sandwiched in a direction parallel to the plane of the substrate 201.

  Also in the seventh embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the cladding layer 204 in the resonator region having a predetermined length in the extending direction of the optical waveguide 221, and a distributed Bragg having a wavelength of 1.55 μm. A reflective structure is constructed. Note that the upper surfaces of the cladding layer 204, the n-type semiconductor layer 205, and the p-type semiconductor layer 206 between the contact layer 207 and the contact layer 208 are protected by a protective film 211. The semiconductor optical device according to the seventh embodiment also forms a distributed feedback laser by forming a non-reflective film (not shown) at both ends of the resonator region.

  The substrate 201 is made of, for example, semi-insulating InP, and the core 202 is made of InGaAsP. The active layer 203 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier layer with a thickness of 9 nm are stacked. The emission wavelength of the active layer 203 is 1.55 μm.

Further, for example, the cladding layer 204 is made of semi-insulating InP, the n-type semiconductor layer 205 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and the p-type semiconductor layer 206. Is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn. Here, in the seventh embodiment, the semiconductor layer 212 is made of, for example, p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn. The semiconductor layer 212 may have a thickness of about 100 nm.

The contact layer 207 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 208 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. The protective film 211 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 205 and the p-type semiconductor layer 206 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 203 and the cladding layer 204 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  The above configuration is the same as that of the fifth embodiment described above except for the semiconductor layer 212. In the seventh embodiment, the semiconductor layer 212 made of p-InP is disposed under the active layer 203. In the configuration of the seventh embodiment, a lateral injection structure with an n-type semiconductor layer 205 and a p-type semiconductor layer 206 sandwiching the active layer 203 in the substrate plane direction is employed. In this lateral injection structure, there is a problem that hole injection becomes non-uniform. To solve this problem, the seventh embodiment uses the p-type semiconductor layer 212. Therefore, even when the waveguide width is wide, uniform current injection can be performed in the lateral direction. Since the electric field almost exists in the waveguide region, there is little overlap between the p-type semiconductor layer 212 and the electric field, and the current injection efficiency can be increased without worrying about the increase in the waveguide loss.

[Embodiment 8]
Next, an eighth embodiment of the present invention will be described with reference to FIG. FIG. 13 is a sectional view showing a semiconductor optical device according to the eighth embodiment of the present invention.

  This semiconductor optical device first includes an optical waveguide 321 composed of a clad layer 304 and a core 302 formed on a substrate 301. The core 302 is embedded in the cladding layer 304. In addition, the active layer 303 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 321 and to be optically coupled to the core 302. In the eighth embodiment, the active layer 303 is layered to have a slab structure.

  In addition, an n-type semiconductor layer 305 and a p-type semiconductor layer 306 formed in contact with the active layer 303 and the cladding layer 304 are provided. In the eighth embodiment, the core 302 is disposed on the active layer 303 when viewed from the substrate 301 side. In the eighth embodiment, current is injected into the active layer 303 in a direction parallel to the plane of the substrate 301.

  In the eighth embodiment, the above-described active layer 303 having the slab structure is disposed between the substrate 301 and the optical waveguide 321.

  Further, an n-type electrode 309 connected to the n-type semiconductor layer 305 through a contact layer 307 and a p-type electrode 310 connected to the p-type semiconductor layer 306 through a contact layer 308 are provided. In the eighth embodiment, the p-type semiconductor layer 306 and the n-type semiconductor layer 305 are formed on the layered active layer 303 when viewed from the substrate 301 side. The p-type semiconductor layer 306 and the n-type semiconductor layer 305 are formed with the optical waveguide 321 interposed therebetween.

  Also in the eighth embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the cladding layer 304 in the resonator region having a predetermined length in the extending direction of the optical waveguide 321, and has a wavelength distribution of 1.55 μm. A Bragg reflection structure is configured. Note that the upper surfaces of the cladding layer 304, the n-type semiconductor layer 305, and the p-type semiconductor layer 306 between the contact layer 307 and the contact layer 308 are protected by a protective film 211. In the semiconductor optical device according to the eighth embodiment, a non-reflective film (not shown) is formed at both ends of the resonator region to constitute a distributed feedback laser.

  The substrate 301 is made of, for example, semi-insulating InP, and the core 302 is made of InGaAsP. The active layer 303 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier thickness of 9 nm are stacked. The emission wavelength of the active layer 303 is 1.55 μm.

Further, for example, the cladding layer 304 is made of semi-insulating InP, the n-type semiconductor layer 305 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and the p-type semiconductor layer 306. Is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 307 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 308 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. The protective film 211 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 305 and the p-type semiconductor layer 306 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 303 and the clad layer 304 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  Next, the dependence of the light confinement around the active layer 303 on the active layer width will be described with reference to FIGS. 14A and 14B. 14A shows the active layer width dependency of optical confinement in the p-type semiconductor layer 206, and FIG. 14B shows the active layer width dependency of optical confinement in the active layer 303. The band gap wavelength of the core 302 was 1.3 μm or 1.4 μm, and the thickness of the core 302 was 350 nm. The distance between the active layer 303 and the core 302 was 100 nm, and the thickness of the clad layer 204 disposed on the active layer 303 was 100 nm. The interval between the core 302 and the p-type semiconductor layer 206 was 500 nm.

  Although the loss in the p-type semiconductor layer 306 is slightly increased as compared with the fifth embodiment, the optical confinement in the p-type semiconductor layer 306 is still 1/10 or less of the pn filling, and the light in the active layer 303 is light. There is an effect of increasing confinement.

[Embodiment 9]
Next, Embodiment 9 of the present invention will be described with reference to FIG. FIG. 15 is a sectional view showing a semiconductor optical device according to the ninth embodiment of the present invention.

  This semiconductor optical device first includes an optical waveguide 321 composed of a clad layer 354 and a core 302 formed on a substrate 301. The core 302 is embedded in the cladding layer 354. In addition, the active layer 303 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 321 and to be optically coupled to the core 302. Also in the ninth embodiment, the active layer 303 is formed in a layer shape to form a slab waveguide structure.

  In addition, an n-type semiconductor layer 305 and a p-type semiconductor layer 306 formed in contact with the active layer 303 and the cladding layer 354 are provided. In the ninth embodiment, the core 302 is disposed on the active layer 303 when viewed from the substrate 301 side. In the ninth embodiment, current is injected into the active layer 303 in a direction parallel to the plane of the substrate 301.

  Here, the active layer 303, the n-type semiconductor layer 305, and the p-type semiconductor layer 306 constitute a slab optical waveguide as described above. In the slab optical waveguide according to the ninth embodiment, the active layer 303 formed in a layer shape serves as a core, and the substrate 301, the clad layer 354, the n-type semiconductor layer 305, and the p-type semiconductor layer 306 serve as a clad. In the ninth embodiment, the above-described slab optical waveguide is disposed between the substrate 301 and the optical waveguide 321.

  Further, an n-type electrode 309 connected to the n-type semiconductor layer 305 through a contact layer 307 and a p-type electrode 310 connected to the p-type semiconductor layer 306 through a contact layer 308 are provided. In Embodiment 9, the p-type semiconductor layer 306 and the n-type semiconductor layer 305 are formed on the layered active layer 303 when viewed from the substrate 301 side. The p-type semiconductor layer 306 and the n-type semiconductor layer 305 are formed with the optical waveguide 321 interposed therebetween.

  Also in the ninth embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the cladding layer 354 in the resonator region having a predetermined length in the extending direction of the optical waveguide 321, and the distribution is 1.55 μm in wavelength. A Bragg reflection structure is configured. Note that the upper surfaces of the cladding layer 354, the n-type semiconductor layer 305, and the p-type semiconductor layer 306 between the contact layer 307 and the contact layer 308 are protected by a protective film 211. In the semiconductor optical device according to the ninth embodiment, a non-reflective film (not shown) is formed at both ends of the resonator region to constitute a distributed feedback laser.

  The substrate 301 is made of, for example, semi-insulating InP, and the core 302 is made of InGaAsP. The active layer 303 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier thickness of 9 nm are stacked. The emission wavelength of the active layer 303 is 1.55 μm.

In the ninth embodiment, the cladding layer 354 is made of, for example, undoped InP, and the n-type semiconductor layer 305 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and p The type semiconductor layer 306 is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 307 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 308 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. The protective film 211 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 305 and the p-type semiconductor layer 306 can be formed by buried regrowth of n-InP and p-InP after forming the active layer 303 and the cladding layer 354 by the above-described patterning or the like. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

  In the ninth embodiment, the cladding layer 354 is made of undoped InP, and the other structure is the same as that of the eighth embodiment described above. Compared with the case of being composed of semi-insulating InP, the current insulation is reduced, but the fabrication becomes easy.

[Embodiment 10]
Next, Embodiment 10 of the present invention will be described with reference to FIG. FIG. 16 is a sectional view showing a semiconductor optical device according to the tenth embodiment of the present invention.

  The semiconductor optical device includes a semiconductor layer 404a, an active layer 403, a semiconductor layer 404b, a core 402, and a semiconductor layer 404c formed on a substrate 401. Here, the semiconductor layer 404b is a lower clad, the semiconductor layer 404c is an upper clad, and a core 402 is sandwiched between them to constitute an optical waveguide 421.

  In the tenth embodiment, the active layer 403 described above is disposed between the substrate 401 and the optical waveguide 421. The active layer 403 extends for a predetermined distance in the waveguide direction of the optical waveguide 421 and is disposed in a state where it can be optically coupled to the core 402. In the tenth embodiment, the core 402 is disposed on the active layer 403 when viewed from the substrate 401 side.

  In addition, an n-type semiconductor layer 405 and a p-type semiconductor layer 406 are provided which are in contact with the active layer 403 and sandwich the active layer 403 therebetween. In the tenth embodiment, the n-type semiconductor layer 405 and the p-type semiconductor layer 406 are formed with an optical waveguide having the active layer 403 as a core therebetween. The n-type semiconductor layer 405 and the p-type semiconductor layer 406 are not formed on both sides of the core 402 and the semiconductor layer 404c.

  Further, an n-type electrode 409 connected to the n-type semiconductor layer 405 by a contact layer 407 and a p-type electrode 410 connected to the p-type semiconductor layer 406 by a contact layer 408 are provided. The p-type semiconductor layer 406 and the n-type semiconductor layer 405 are formed with the active layer 403 sandwiched in a direction parallel to the plane of the substrate 401. In the tenth embodiment, current is injected into the active layer 403 in a direction parallel to the plane of the substrate 401. Further, as described above, since the n-type semiconductor layer 405 and the p-type semiconductor layer 406 are not formed on both sides of the core 402, current injection into the core 402 is suppressed. It becomes like this. For this reason, there is no need to worry about current leakage.

  In the tenth embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the semiconductor layer 404c in the resonator region having a predetermined length in the extending direction of the optical waveguide 421, and a distributed Bragg having a wavelength of 1.55 μm. A reflective structure is constructed. Note that the upper surface of the semiconductor layer 404 c is protected by a protective film 411. The semiconductor optical device according to the tenth embodiment also forms a distributed feedback laser by forming a non-reflective film (not shown) at both ends of the resonator region.

  The substrate 401 is made of, for example, semi-insulating InP, and the core 402 is made of InGaAsP. The active layer 403 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked.

Further, for example, the semiconductor layer 404a, the semiconductor layer 404b, and the semiconductor layer 404c are made of undoped InP, and the n-type semiconductor layer 405 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si. The p-type semiconductor layer 406 is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 407 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 408 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. Further, the protective film 411 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The n-type semiconductor layer 405 and the p-type semiconductor layer 406 are formed by the n-InP and p- after the semiconductor layer 404a, the active layer 403, the semiconductor layer 404b, the core 402, and the semiconductor layer 404c are formed by the above-described patterning or the like. It can be formed by buried regrowth of InP. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

[Embodiment 11]
Next, an eleventh embodiment of the present invention will be described with reference to FIG. FIG. 17 is a sectional view showing a semiconductor optical device according to the eleventh embodiment of the present invention.

  The semiconductor optical device includes a semiconductor layer 404a, an active layer 403, a semiconductor layer 404b, and a core 412 formed on a substrate 401. Here, in the eleventh embodiment, the core 412 is made of amorphous silicon, and the optical waveguide 421a is formed with the periphery as a clad.

  Also in the eleventh embodiment, the core 412 is disposed on the active layer 403 when viewed from the substrate 401 side.

  In addition, an n-type semiconductor layer 405 and a p-type semiconductor layer 406 are provided which are in contact with the active layer 403 and sandwich the active layer 403 therebetween. In the eleventh embodiment, the n-type semiconductor layer 405 and the p-type semiconductor layer 406 are formed with an optical waveguide having the active layer 403 as a core therebetween. The n-type semiconductor layer 405 and the p-type semiconductor layer 406 are not formed on both sides of the core 412.

  Further, an n-type electrode 409 connected to the n-type semiconductor layer 405 by a contact layer 407 and a p-type electrode 410 connected to the p-type semiconductor layer 406 by a contact layer 408 are provided. The p-type semiconductor layer 406 and the n-type semiconductor layer 405 are formed with the active layer 403 sandwiched in a direction parallel to the plane of the substrate 401. In Embodiment Mode 11, current is injected into the active layer 403 in a direction parallel to the plane of the substrate 401.

  Further, as described above, the n-type semiconductor layer 405 and the p-type semiconductor layer 406 are not formed on both sides of the core 412, so that current is suppressed from being injected into the core 412. It becomes like this. For this reason, there is no need to worry about current leakage. In addition, since the core 412 can be formed by a technique such as sputtering or CVD without using crystal growth, a waveguide can be easily formed.

  In the eleventh embodiment, a diffraction grating pattern (not shown) is formed on the upper surface of the semiconductor layer 404b in the resonator region having a predetermined length in the extending direction of the optical waveguide 421a, and a distributed Bragg having a wavelength of 1.55 μm. A reflective structure is constructed. In this configuration, the upper surface of the semiconductor layer 404 b is protected by the core 412. The semiconductor optical device in the eleventh embodiment can also be a distributed feedback laser by forming a non-reflective film at both ends of the resonator region. Note that the diffraction grating may be formed in the core 412.

  The substrate 401 is made of, for example, semi-insulating InP, and the core 412 is made of InGaAsP. The active layer 403 has a quantum well structure in which eight layers of a 6 nm thick well layer and a 9 nm thick barrier layer made of InGaAsP are stacked.

Further, for example, the semiconductor layer 404a and the semiconductor layer 404b are made of undoped InP, and the n-type semiconductor layer 405 is made of n-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Si, and is a p-type semiconductor. The layer 406 is made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn.

The contact layer 407 is made of n-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Si, and the contact layer 408 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. Has been. Further, the protective film 411 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. In addition, the n-type semiconductor layer 405 and the p-type semiconductor layer 406 are embedded in the n-InP and p-InP after the semiconductor layer 404a, the active layer 403, the semiconductor layer 404b, and the core 412 are formed by the above-described patterning or the like. It can be formed by growth. In addition, after forming each part by burying regrowth of undoped InP, these impurities may be introduced by introducing impurities by ion implantation or a thermal diffusion method.

[Embodiment 12]
Next, Embodiment 12 of the present invention will be described with reference to FIG. FIG. 18 is a sectional view showing a semiconductor optical device according to the twelfth embodiment of the present invention. Hereinafter, a case where current is injected into the active layer in a direction perpendicular to the plane of the substrate will be described.

  This semiconductor optical device first includes an optical waveguide 521 including a cladding layer 501 and a core 522. The core 522 is embedded in the cladding layer 501. Although not shown, the cladding layer 501 is formed on the substrate. In addition, the active layer 503 is provided so as to extend a predetermined distance in the waveguide direction of the optical waveguide 521 and to be optically coupled to the core 522. Here, the core 503 is formed on the n-type semiconductor layer 502, and the p-type semiconductor layer 508 is formed on the core 503.

  Further, a part of the n-type semiconductor layer 502 and the core 503 are formed in a mesa shape, and both sides thereof are embedded in the p-type embedded semiconductor layers 504 and 505. In addition, n-type current blocking layers 506 and 507 are formed on the p-type buried semiconductor layers 504 and 505. The p-type semiconductor layer 508 is formed over the core 503 and the n-type current blocking layers 506 and 507.

  Further, a p-type electrode 511 connected by a contact layer 509 is formed on the p-type semiconductor layer 508. Here, an insulating layer 510 is formed between the p-type electrode 511 and the contact layer 509 other than the region where the active layer 503 is formed. Further, an n-type electrode 512 is connected to an n-type semiconductor layer 502 formed extending from the formation region of the p-type buried semiconductor layers 504 and 505.

  In this semiconductor optical device, the n-type semiconductor layer 502 and the p-type semiconductor layer 508 are configured to inject current into the active layer 503 in a direction perpendicular to the plane of the substrate. Even with this structure, a narrow linewidth laser can be realized.

  The substrate (not shown) and the cladding layer 501 are made of, for example, InP made semi-insulating by doping iron, and the core 522 is made of InGaAsP. The active layer 503 has a quantum well structure in which eight layers of a well layer made of InGaAsP with a thickness of 6 nm and a barrier layer with a thickness of 9 nm are stacked. The emission wavelength of the active layer 503 is 1.55 μm.

For example, the n-type semiconductor layer 502 is made of n-InP doped with Si by about 1 × 10 ¹⁸ cm ⁻³ , and the p-type semiconductor layer 508 is doped with Zn by about 1 × 10 ¹⁸ cm ^−3. P-InP. The p-type buried semiconductor layers 504 and 505 are made of p-InP doped with about 1 × 10 ¹⁸ cm ^{−3 of} Zn, and the n-type current blocking layers 506 and 507 are made of Si of 1 × 10 ¹⁸ cm ^{−. It} consists of n-InP doped about ³ times.

The contact layer 509 is made of p-InGaAs doped with about 1 × 10 ¹⁹ cm ^{−3 of} Zn. The insulating layer 510 is made of, for example, SiO ₂ .

  Each compound semiconductor layer is formed, for example, by crystal growth by a well-known metal organic chemical vapor deposition method. In addition, each of the waveguide structures and the diffraction grating is formed by using a known lithography technique and patterning by wet etching or dry etching. The p-type buried semiconductor layers 504 and 505 and the n-type current blocking layers 506 and 507 are formed by buried regrowth of n-InP and p-InP after the active layer 503 and the like are formed by the above-described patterning or the like. Can do.

[Embodiment 13]
Next, Embodiment 13 of the present invention will be described with reference to FIG. FIG. 19 is a sectional view showing a semiconductor optical device according to the thirteenth embodiment of the present invention.

  This semiconductor optical device includes an optical waveguide 521 including a cladding layer 501a, a core 532, and a cladding layer 501b. The core 532 has a layered shape and is sandwiched between the cladding layer 501a and the cladding layer 501b. Other configurations are the same as those of the twelfth embodiment. According to the thirteenth embodiment, since the core 532 does not have an embedded structure, an embedding process is unnecessary, and device fabrication is facilitated.

[Embodiment 14]
Next, a fourteenth embodiment of the present invention will be described with reference to FIG. FIG. 20 is a sectional view showing a semiconductor optical device according to the fourteenth embodiment of the present invention.

  The semiconductor optical device includes an optical waveguide 521 including a cladding layer 501, a core 522, and an upper cladding layer 523. The core 522 is embedded in the cladding layer 523 on the cladding layer 501. The upper cladding layer 523 may be made of undoped InP. Other configurations are the same as those of the twelfth embodiment. According to the fourteenth embodiment, similar to the fourth embodiment described above, the embedding process with high resistance InP is unnecessary, and the device fabrication is facilitated.

  As described above, according to the present invention, apart from the optical waveguide made of the core, an active layer is provided that extends in the waveguide direction of the optical waveguide for a predetermined distance so as to be optically coupled to the core. Since the p-type semiconductor layer and the n-type semiconductor layer are formed in contact with the active layer, the waveguide loss in the semiconductor optical device having the buried waveguide structure can be reduced.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

For example, in the above description, the active layer is made of InGaAsP. However, the present invention is not limited to this, and it goes without saying that other optical semiconductor materials such as InAlGaAs are applicable. The operating wavelength is not limited to 1.55 μm, and can be freely designed by selecting a material. In the form of the diffraction grating, the diffraction grating pattern is formed in the upper semiconductor layer. However, the diffraction grating pattern may be formed in a protective film made of SiN, SiO ₂ or the like formed in the upper layer. Needless to say, a buried diffraction grating can be formed on the core or the active layer. Although the DFB laser structure has been described as an example, the present invention is not limited to this, and the present invention is to realize a waveguide for an active layer with a low waveguide loss. The active layer region of other lasers, It is also clear that it can be applied as an optical amplification region.

  DESCRIPTION OF SYMBOLS 100 ... Substrate, 101 ... Clad layer, 102 ... Core, 103 ... Active layer, 104 ... Semiconductor layer, 105 ... N-type semiconductor layer, 106 ... P-type semiconductor layer, 107 ... Contact layer, 108 ... Contact layer, 109 ... n 110, p-type electrode, 111, protective film, 121, optical waveguide, 131, resonator region, 132, diffraction grating pattern.

Claims (6)

An optical waveguide comprising a core formed on a substrate;
An active layer extending in a waveguide direction of the optical waveguide and arranged in a state capable of optically coupling with the core;
A p-type semiconductor layer and an n-type semiconductor layer formed in contact with the active layer;
A semiconductor layer formed in contact with at least one of the lower surface and the upper surface of the active layer;
An n-type electrode connected to the n-type semiconductor layer;
A p-type electrode connected to the p-type semiconductor layer ,
The p-type semiconductor layer and the n-type semiconductor layer are formed with the active layer sandwiched in a direction parallel to the plane of the substrate,
Current is injected into the active layer in a direction parallel to the plane of the substrate,
The core semiconductor optical device characterized that you have been formed spaced from the p-type semiconductor layer. The semiconductor optical device according to claim 1,
The semiconductor optical device, wherein the core is disposed between the substrate and the active layer. The semiconductor optical device according to claim 2 ,
The semiconductor optical element , wherein the semiconductor layer formed in contact with the upper surface of the active layer has a side surface in contact with the p-type semiconductor layer and the n-type semiconductor layer and is p-type . The semiconductor optical device according to claim 1,
The semiconductor optical device, wherein the core is disposed on the active layer when viewed from the substrate side. The semiconductor optical device according to claim 4,
The semiconductor optical element formed in contact with the lower surface of the active layer has a side surface in contact with the p-type semiconductor layer and the n-type semiconductor layer and is p-type . The semiconductor optical device according to any one of claims 1 to 5 ,
The p-type semiconductor layer and the n-type semiconductor layer, a semiconductor optical device characterized by that formed from InP.